The present invention relates to a method for producing a radio wave-transmitting wavelength-selective plate that can efficiently transmit radio waves and visible light rays arriving at window glasses of buildings, automobiles and the like and that exhibits a sufficient heat insulation by reflecting heat rays of the sun.
In recent years, window glasses covered with conductive thin films or window glasses having films coated with conductive thin films have begun to prevail, for the purpose of shielding solar radiation.
The application of such window glasses to high buildings reflects radio waves of TV frequency band and causes the occurrence of ghost on the TV screen. Furthermore, it becomes difficult to receive satellite broadcast using an indoor antenna.
Furthermore, in case that they were used as residential window glasses or automotive window glasses, the communication with mobile phones was likely to become difficult, and it became a cause to lower the gain of an indoor antenna or glass antenna formed on vehicular window glass.
Under such condition, it is now conducted to coat a glass substrate with a transparent heat ray reflecting film of a relatively high electric resistance to transmit a part of the visible light rays and to reduce the radio wave reflection to prevent radio interference.
For example, in the case of a glass with a conductive film, it is known to prevent radio interference by partitioning the conductive film coated on a glass substrate such that the length of the conductive film that is parallel with the field direction of the incident radio wave is made to be 1/20 or less times the radio wave wavelength (see Japanese Patent No. 2620456).
Although the above method of coating thereon a transparent heat ray reflecting film of a relatively high electric resistance can prevent radio interference by reducing the radio wave reflection, the heat ray shielding performance was not sufficient, and it was problematic in terms of the life amenity.
Furthermore, a method of partitioning a conductive film is disclosed in Japanese Patent Laid-open Publication 2000-281388. Since the partition length is much longer than the wavelengths of the visible light and near infrared light occupying a most part of the sun light, all of these lights are reflected. Although there is obtained a radio-transmitting, wavelength-selective screen glass that prevents radio interference and has a sufficient solar radiation shielding performance, there is a problem of not being capable of maintaining the visible light transmission. Furthermore, in a large window having an opening size of 2 m×3 m, for example, it is necessary to cut a conductive film to 1/20 of the wavelength (about 25 mm) of satellite broadcast, at least to 1.25 mm squares, preferably 0.5 mm squares, in order to transmit satellite broadcast waves. It is necessary to take a long time to cut a large-area conductive film into such small segments by means of, for example, an yttrium-aluminum-garnet laser. Thus, it had problems such as being unrealistic.
Thus, the present inventors and others proposed a radio wave-transmitting, wavelength-selective plate in which fine particles composed of Ag are formed on a transparent substrate (see Japanese Patent Laid-open Publication 2000-281388).
There was a trouble that spectral reflectance becomes low in the entire wavelength region by shifting a wavelength (hereinafter abbreviated as resonance wavelength) at which spectral reflectance reaches a maximum to a range of 700 nm to 1500 nm, in a radio wave-transmitting, wavelength-selective glass in which granular Ag is formed on a transparent substrate, in order to increase a near infrared shielding coefficient (Es) defined in the formula (1), as disclosed in Japanese Patent Laid-open Publication 2000-281388.